Power management in modern computer systems plays an important part in conserving energy, managing heat dissipation, and improving system performance. Modern computers systems are increasingly designed to be used in settings where a reliable external power supply is not available making power management to conserve energy important. Even when reliable external power supplies are available careful power management within the computing system can reduce heat produced by the system enabling improved performance of the system. Computing systems generally have better performance at lower ambient temperatures because key components can run at higher speeds without damaging their circuitry. Many computing platforms are constrained by heat dissipation issues including dense servers, DT computers and mobile computers. For mobile computers, energy conservation is especially important to conserve battery power.
Power management can also reduce the operating costs of a computing system by reducing the amount of energy consumed by a device while in operation. Components of a computer system can be powered down or put in a sleep mode that requires less power than active operation. Computer monitors are often placed in a sleep mode when an operating system detects that the computer system has not received any input from a user for a defined period of time. Other system components can be placed in a sleep or powered down state in order to conserve energy when the components are not in use. The computer system monitors input devices and wakes devices as needed.
For example, a PCI bus uses a centralized mechanism to determine if the bus is not needed which involves all other devices verifying that they do not need the bus. This system is implemented using out-of-band signaling, thus requiring specialized communication lines in addition to data lines. When the bus is determined not to be needed then the common clock signal is no longer transmitted.